Both ATP and GTP phosphorylate a small fraction of the opsin in light-exposed bovine rod outer segments. This fraction is not identical with newly-synthesized opsin. Attempts will be made to determine whether the small fraction of rhodopsin that acts as a galactose and fucose acceptor is the same fraction that is selectively phosphorylated. The sub-cellular localization of chemically distinct fractions of rhodopsin will aid in elucidating the functions of the outer segment related to both the visual cycle and photoreceptor outer segment renewal.